Stainless bolts

Garden variety 300 series stainless bolts should probably not be used. You may gall the threads if torqued correctly, or even fail the fastener by fracture. If using stainless for this application, you would be better off having them made from a 416 or 420 stainless that has been heat treated to grade 8, or use an age-hardened 17-4 ph stainless to make them. There may be hardened 400 series fasteners on the market but I'm not sure about that.

A decent alternative is to use standard Grade 8 fasteners and have them treated for corrosion resistance, like black oxided or, better yet, nitirided. Best of luck, Brad

It's not as if the stock bolts are that strong either.

Fasteners

BADVOC, I've not heard of an "A2 stainless" steel. In the US of A, A2 is a tool steel; a cold work die steel to be precise, and is not stainless. It is capable of very high strength, but I would consider it too brittle for a torqued fastener. A lower carbon content tool steel like S7 would make a very high strength fastener. H13 even better. But stainless needs to be heat treated to make a good sprocket bolt, and that requires a 400 series stainless as stated previously in this thread. The sprocket bolts I get from the dealer seem to be grade 8 or better, but I only use them once. A nice set of hardened stainless fasteners should be re-uable in my book, but I'm thinking most riders do not want to risk it and simply replace them with each sprocket replacement. Your concerns are quite valid; I've seen the results of loose sprocket bolts first hand. Not pretty. Brad

Fasteners

Sorry, I dodn't answer your question. That MC6S business is a bolt style/head design callout and does not signify the grade of steel used. Brad

http://www.americanfastener.com/technical/grade_markings_steel.asp

Metric grade 8.8 is equivalent to SAE grade 5.

Metric grade 10.9 is equivalent to SAE grade 8.

Metric grade A2-70 (d>=M2) is Metric grade 8.8, SAE grade 5, 304 Stainless steel.

Metric grade A4-70 (d>=M2) is Metric grade 8.8, SAE grade 5, 316 Stainless steel (less strong, more corrosion resistant than A2).

Metric grade A2-50 (d<M2) is Metric grade 8.8, SAE grade 5, 304 Stainless steel.

Most Stainless hardware is Metric 8.8. I haven't actually seen SS Metric 10.9 before.

Metric grade A2 is 304 stainless steel. A4 is 316 stainless steel.

Most Metric 10.9 hardware is not stainless, but coated with zinc (gives it a yellow/gold color)

American Grade 8 hex head hardware typically has a black coating, presumably to prevent corrosion.

I use Metric grade 8.8 everywhere on my Bergs, except where factory harware is more applicable (for instance, the BIG cylinder studs). All my engine side covers and rocker cover use A2 SS hardware.

The big issue to worry about with SS fasteners and aluminum is galvanic corrosion. Due to the metals being dissimilar, they will act as a battery with one another, with one being positive and one being negative. In these circumstances, corrosion occurs. If you leave the SS fasteners in the aluminum block for a long time, you'll have an issue. But, I think you'd be fine if you replaced all fasteners when you do a rebuild every 1-2 years. I also use oil on the bolts when installing, which I think helps a tad bit.

Another issue to worry about with fasteners, as BD mentioned, is galling. This happens when you have two similar metals (steel-steel) directly against one another without any coating on either. This is bad, and should be avoided. Luckily, you'll have a hard time finding uncoated hardware, so it isn't too big of a deal.

The rear caliper (I think) has 6x 8mm hex bolts. If you used SS there, you'd probably be fine, but would be better suited to a higher grade coated cap screw or hex head.

Anyone correct me if I've made a mistake.

-Parsko

fasteners

Parkso, thanks for clarification on the A2-70 fasteners. I see they are stainless, but SAE does not address Grade 5 in anything other than carbon or low alloy steel. Grade 5 is specifically a heat treated, medium carbon steel., (like AISI 1045). Another specification organization, ASTM, does address stainless fasteners, and if you look at ASTM A193, you will find many stainless fastener grades listed, and this is not the only ASTM spec. that addresses fasteners.

While some 304 or 316 stainless fasteners in the US may in fact meet the strength levels of SAE Grade 5, I think most would actually be closer to a Grade 2. The yield strength of SAE Grade 5 is 92,000 PSI for small fasteners, and the A2-70 is, well, 70,000 PSI, (minimums by the way).

I hope this clarifies material grade versus strength grade a little bit. Bolts intended to be significantly torqued, like sprocket bolts, should be a heat treated product. Grade 5 bolts at 10mm, (metric grade 8.8), can be safely torqued to 30 ft lbs. Grade 8, (metric grade 10.9), can be torqued to 45 ft lbs. These are dry bolt values. I'm sure someone has a Berg manual handy and can look up the torque value specified for those fastners by the manufacturer. That will be a good clue as to how strong they should be. BD

It just occured to me, after reading your post, the other drawback of stainless. I think it creeps over time. The heat cycling don't help the situation either.

Loctite should help with the galvanic corrosion and galling on installation. I certainly use it on all hardware on my berg. --> Gotta use loctite <--

Upon further research, I found this interesting chart supporting your argument, BD. Though, if you look at the link I had above, the numbers seem a bit different.



What other information could we include regarding hardware? This would be good reading for the Owner's Doc!...

-Parsko

Yes, it does help. Supermoto will induce higher forces on the sprockets, due to the higher amount of grip available. No, you fool, you'll kill yourself when they snap off. Get grade 8 or equiv!!

-Parsko

As a tangent: I keep reading that a snap from being on throttle to off throttle is bad, and seems to be causing a lot of failure in the motors, specifically the bearings. Similar issue with high forces (basically throughout the hole motor and drivetrain) during rapid changes in throttle. These other guys were mostly going from really fast, long suspended runs, to a quick closing of the throttle.

I wonder if it would not be better for a bolt to not be too hard as to break instead of going through the case and splitting it?

http://www.engineeredracingproducts.com/art/art1.htm

Almost too much useful information in that link.

Badvoc, I'd say, that if the titanium bolts were free, then buy them. If you platinum card is bored, then buy them. But, I think you're better off going with a standard issue grade 8 steel fastener.

As we said, it is your call. 6 (or 8 ) M8 stainless bolts are a lot of strength, even under the conditions seen holding on the sprocket.

-Parsko